Medical molecular imaging originated from the field of radio pharmacology due to the need to better understand the fundamental molecular pathways inside organisms in a noninvasive manner. In a process of molecular imaging, probes known as biomarkers are used to help image particular targets or pathways. Biomarkers interact chemically with their surroundings and in turn alter the image according to molecular changes occurring within the area of interest. It enables the visualization of the cellular function and the follow-up of the molecular process in living organisms without perturbing them. This ability to image fine molecular changes opens up an incredible number of exciting possibilities for medical application, including early detection and treatment of disease and basic pharmaceutical development. However, no matter it is for the development and evaluation of new drugs using molecular imaging research, or for the evaluation upon the effectiveness of a SPECT system, a PET system, or a MRI system, a good biological phantom is required.
In order to obtain clinically realistic images in a quantitative medical research in drug development and evaluation, anthropomorphic phantoms are generally used and required. Among which lesion phantoms which represent areas of interest are oftentimes the focal points of many quantitative medical evaluations, such as the quantification and assessment of drug absorption rate in lesions, the calibration of medical imaging upon lesions, the evaluation of how the amount of drug absorption can affect the threshold setting in a medical imaging for lesion detection.
There are two types of lesion phantoms currently available on the market. Among which, the type that is referred as “cold phantom” is a phantom formed without contrast agent/medicine reservoir and is generally a solid structure made of a tissue-mimicking material; while another type is referred as “hot phantom”, that is a phantom formed with contrast agent/medicine reservoir and is generally a hollow structure made of a tissue-mimicking material. Comparatively, the hot phantom is more flexible in usage as it is able to simulate lesions of different absorption rates, and also can be used as a “cold phantom” while having its cavity to be filled with certain non-active materials.
In any phantom study for quantitatively evaluating and assessing a medical imaging system in drug development and evaluation, the accuracy of lesion signal caused by the hot phantom is most valued since any minute error in the reading of the lesion signal may be of serious consequence in the drug development and evaluation. Accordingly, the accuracy of lesion signal is severely dependent upon the accuracy of the hot phantom, not just in the accuracy relating to the volume of the phantom, but also in the accuracy relating to the amount of contrast agent or medicine that are to be fed into the cavity of the hot phantom. It is noted that a good lesion phantom should be able to be used repetitively while allowing each injection and removal of contrast agent to be performed accurately in volume and with high degree of repeatability. However, such accuracy and good repeatability are not achievable by the phantoms that are currently available on the market. Generally, after several repetitive injections and removals of contrast agent, the probability of signal contamination, i.e. signals being generated at positions where are not expected, or radioactive contamination, i.e. the extravasation of radioactive contrast agent or medicine, is often increased exponentially. In addition, with regard to the positioning of lesion phantom, the usage of those phantoms that are currently available on the market are not flexible in that they are fixed to be secured at only a few specific positions and cannot be changed at will. Furthermore, the internal diameter of the smallest lesion phantoms that are currently available on the market is still 3.95 mm, which is not small enough to be in many medical imaging researches. Thus, the lesion phantoms that are currently available on the market are known to be insufficient in accuracy, ease-of-use, usage flexibility, and reality, and therefore, they are required to be improved.
Please refer to FIG. 4, which is a schematic diagram showing a prior-art breast phantom by Data Spectrum Cooperation. Nevertheless, each lesion phantom 1 in FIG. 4 is still being fixed to one specific position at its corresponding breast that it is not allowed to be changed at will. Please refer to FIG. 5, which is a schematic diagram showing a spherical lesion phantom used in the breast phantom of FIG. 4 that is filled with a contrast agent. In FIG. 5, the spherical lesion phantom 1′, being a “hot phantom”, can be filled with a contrast agent 8′ through injection using a needle. However, it is noted that such spherical lesion phantom 1′ sill has problems, e.g. the overflowing of contrast agent 8′ is not preventable, as shown in FIG. 6, and also there can be bubbles 9′ trapped inside the spherical lesion phantom 1′, as shown in FIG. 7. In addition, since the fixing bar 7′ is fixedly secured to the sphere 2′ of the lesion phantom 1′ by screwing the external thread 71′ formed on the fixing bar 7′ to mate with the internal thread 31′ formed inside the extension tube 3′ of the sphere 2′, such fixing manner can easily cause the residue contrast agent 8′ at the interface between the lesion phantom 1′ and the external thread 71′ to be squeezed and thus overflow. Therefore, the problems including the signal contamination, i.e. signals being generated at positions where are not expected, and radioactive contamination, i.e. the extravasation of radioactive contrast agent, cannot be prevented during the performing of a medical imaging research.
Moreover, as the fixing bar 7′ is made of a specific size, especially in length, that it is not adjust able in length, the lesion phantom 1′ can only fixed to a specific position inside the breast phantom. In addition, the internal diameter of the sphere 2′ of the lesion phantom 1′ is about 3.95 mm that it is not able to mimic tumors or lesions smaller than that.
Therefore, it is in need of a lesion phantom capable overcoming the aforesaid shortcomings